1. The Field of the Invention
The present invention relates generally to data communications. More specifically the present invention relates to apparatus and methods for attenuating signals received from a data transmission line in a data communications environment to achieve optimized signals for processing.
2. The Relevant Technology
In a data communications environment, data is communicated from a sender (data source) to a receiver (data sink) over a data link. In general, the data link includes the transmission medium, such as a wire, appropriate transmission and receiving devices and any intermediary routing devices.
With reference to FIG. 1, a basic conventional embodiment of a data communications environment for communicating data from a sender to a receiver is depicted generally as 20. In this embodiment, as indicated by arrow 22, data is communicated from a data source at one end of the data communications environment to a data sink at another end of the data communications environment. As depicted, a typical data source and sink includes some form of a data terminal equipment (DTE) device 24, such as a terminal or a computer, interfaced with one or more data communications equipment (DCE) devices 26, such as a modem. All are well known in the art.
Electronically separating the data source and the data sink is a transmission medium. typical transmission media include, but are not limited to, wire lines, optical fibers and air. In this embodiment, the transmission medium is a transmission line 28, such as an insulated conductive telephone line found frequently in a plain old telephone service (POTS) system for carrying voice and data signals.
Frequently, an intermediary handler of the data, indicated as node 30, is used to facilitate the data transmission between the data source and data sink. Typical intermediary handlers provide services such as switching functions to route data along an optimized path, mediation handling to modify the data into proper transmission protocols, store-and-forward handling to hold data for a predefined amount of time or more sophisticated services such as time and frequency multiplexing. As an example, a central office 32 in a POTS system serves to provide some or all of the foregoing services.
The physical distance of the transmission line between the intermediary handler and either the data source or sink, however, may range from a few hundred feet to several miles. As is known, this distance causes attenuation in the signal strength of the transmitted data. In general, the greater the distance, the greater the attenuation, and vice versa. As a result, the data sink receives, and must process, data signals having had great attenuation or little to no attenuation. This causes restrictions in the dynamic range of specific DTE and/or DCE devices. For example, an analog-to-digital converter (ADC) in a modem must conventionally accept and process input signals supplied with signal strengths in a range from xe2x88x929 dbm to as little as xe2x88x9245 dbm.
Accordingly, it would be an advance to overcome the foregoing transmission line attenuation problems and optimize the signals supplied to various data terminal and data communications equipment in a data communications environment.
It is, therefore, an object of the present invention to provide apparatus and methods for attenuating signals received from a data transmission line in a data communications environment.
It is another object of the present invention to provide apparatus and methods for optimizing signals supplied via a data transmission line to data terminal and communications equipment in a data communications environment.
It is still another object of the present invention to provide a modem having means for attenuating signals supplied from a data transmission line in a data communications environment to an internal ADC to achieve signals at the ADC having optimized signal strengths.
It is yet another object of the present invention to provide the foregoing in an economical manner.
In accordance with the invention as embodied and broadly described herein, the foregoing and other objectives are achieved by providing apparatus and methods for attenuating signals received via a data transmission line. An unknown resistance of the transmission line is determined which ultimately leads to the optimization of the signals in various data terminal and data communications equipment.
In a preferred embodiment, a resistor network is operably coupled between the transmission line and a means for processing the signal, such as a digital processor. The resistor network comprises a termination resistor that is associated with a termination voltage, a variable resistor and another resistor.
During use, a switch is operably positioned between a plurality of switch positions so that two voltage measurements will lead to the determination of the voltage of the data source and the termination voltage within the resistor network. Once these voltages are known, the unknown resistance of the transmission line can be estimated. Thereafter, the length of the transmission line may be determined because of known resistance-per-unit-distance characteristics of the transmission line. In response to knowing this length, the digital processor selects a desired resistance value for the variable resistor so that, upon adjustment of the variable resistor, the signal is optimized for processing at the digital processor.
In a more particular embodiment, the digital processor selects the desired resistance value for the variable resistor and a digital-to-analog convertor serves to adjust the variable resistor. Thereafter, the signal is optimized for processing at an input of an analog-to-digital convertor before being supplied to the digital processor.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.